Deficiency Anemia
During pregnancy, hemoglobin (Hb) and hematocrit (Hct) levels decrease physiologically due to an expansion of blood volume by approximately 50% and red blood cell mass by only approximately 25% [
45]. Pregnant women need to mobilize additional iron to meet the requirements of the growing fetoplacental unit, amounting to 1,200 mg during the course of pregnancy [
46]. Although the absorption of iron is increased during pregnancy, it seems that an appropriate diet alone is not sufficient to meet those requirements, especially for women with a low pre-pregnancy iron status (Ferritin level < 30 μg/L) [
47]. Thus, iron-deficiency anemia (IDA) is the most frequent form of anemia in pregnant women. According to the WHO, anemia, defined as Hb levels of < 11 mg/dl in pregnant women, affects 41.8% of this population subgroup worldwide, with iron deficiency accounting for approximately 50% of cases [
48].
There also seems to be a link between obesity and an altered iron metabolism. Obesity is considered to be a state of chronic inflammation, leading to increased levels of the acute-phase reactant hepcidin which inhibits the enterocyte iron absorption. Other factors such as inflammatory-induced sequestration of iron to the reticuloendothelial system and higher iron requirements due to larger blood volume add to the association between obesity and hypoferremia [
49].
Weight loss after BS results in falling serum hepcidin levels and potentially improved iron status [
50]. Patients who underwent malabsorptive surgery, however, showed an increase in anemia rates (anemia prevalence from 12.2% at baseline to 25.9% after 2 years, prevalence of low ferritin levels from 7.9% at baseline to 23.0% after 2 years) which can be attributed to a reduced caloric intake, intolerance for red meat, reduced acid production of the stomach and subsequently decreased bioavailability of dietary iron and the bypass of food through the duodenum [
26]. A history of BS before pregnancy seems to increase the risk for the development of IDA during pregnancy [
51,
52]. One study indicates that the rate of severe anemia might be higher in pregnancies that occur more than 4 years after RYGB surgery, leading to the conclusion that the time to conception might also be of importance [
53]. However, all studies on the topic have limitations and further research is required to reinforce the currently available supplementation recommendations for the prevention of IDA in pregnant women after BS [
22,
52,
54]. As IDA during pregnancy has adverse effects on pregnancy outcome (e.g. an increased risk for preterm delivery [
55,
56]), prevention is however crucial. Also, maternal iron deficiency seems to have long term health effects on the offspring, mainly neurobehavioral abnormalities and an elevated cardiovascular disease risk [
46,
57]. The ACOG recommends a daily intake of 27 mg of ferrous iron during pregnancy for patients without a history of BS [
45], the WHO recommends 30 to 60 mg of elemental iron [
58]. According to the current literature, the recommended supplementation dose for the prevention of IDA in non-pregnant women with a history of BS is 45 to 130 mg iron daily [
59,
60], whereas the currently available recommendation for pregnant women after RYGB ranges from 40 to 600 mg of ferrous iron daily [
24,
61,
62]. Any dose within this range should therefore be applicable; however, frequent laboratory tests should be performed and the dose adapted according to the results [
61,
62]. The ACOG recommends a complete blood count and measurement of iron and ferritin every trimester [
23].
Folic acid and Vitamin B12 deficiency can also lead to maternal anemia. The folic acid demand increases from 50 to 400 μg per day during pregnancy and cannot always be met by diet alone, leading to folic acid deficiency being the most common cause for macrocytic anemia (MCV > 100 fL) during pregnancy [
45]. Folic acid deficiency seems to be rare after all BS procedures [
26,
63,
64]. The Endocrine Society Clinical Practice Guideline recommends biochemical monitoring preoperatively and 6, 12, 18 and 24 months after surgery and then in annual intervals only for patients after malabsorptive or combined procedures. A daily supplement of 400 μg of folic acid should also be performed [
59]. The American Association of Clinical Endocrinologists also recommends pre- and postoperative routine screening only for patients after malabsorptive or combined BS and also a daily supplement of 400 μg of folic acid for all women of reproductive age [
60]. Gascoin et al. compared non-obese pregnant controls with pregnant women after gastric bypass who took 800 μg/day of folic acid and did not observe folic acid deficiency in the bariatric group [
63]. Weng et al. could also find no evidence of folate deficiencies in patients after RYGB. They suggest that folate absorption occurs throughout the entire small intestine and any deficiency caused by inadequate dietary intake can therefore easily be corrected by supplementation [
26]. Jans et al. report folate deficiency in 0 to 16% of pregnancies after BS with no adverse clinical outcomes [
54]. As there is still controversy regarding the benefit of folic acid supplementation on pregnancy outcomes [
65], it seems prudent to follow the general folic supplementation recommendations for pregnant women and screen for folate deficiency every trimester [
60]; which is also supported by the ACOG [
23].
Vitamin B12 deficiency anemia is mostly seen in women after gastric resection or with Crohn’s disease [
45]. The additional requirement of vitamin B12 during pregnancy is estimated to be 0.2 μg/day [
66]. Vitamin B12 deficiency seems to occur especially after malabsorptive or combined BS as the secretion of intrinsic factor and gastric acid is decreased and the duodenum, being the main absorption site, is bypassed. Incidence of Vitamin B12 deficiency after RYGB is reported to be between 4 and 62% [
59,
67], with a tendency to increase over the course of time, possibly due to the fact that the body’s reserves are able to cover the decreased absorption at early stages [
26]. In pregnant women after BS, the prevalence of Vitamin B12 deficiency is reported to be between 48 and 53% [
54], but not in bariatric gravidas who received a Vitamin B12 supplementation of 4 μg/day and 1,000 μg/month [
63]. The Endocrine Society recommends biochemical monitoring preoperatively; 6, 12, 18 and 24 months after surgery and then in annual intervals only for patients after malabsorptive or combined procedures. With regards to the supplementation dose, recommendations for non-pregnant individuals range from 1,000 μg intramuscularly (im) every 3 months to 1,000 μg/week intranasally [
59]. The American Association of Clinical Endocrinologists recommends pre-operative and annual screening for Vitamin B12 deficiency in patients after malabsorptive and combined bariatric procedures and a supplementation of 1,000 μg/day orally or 500 μg/week intranasally or 1,000 μg/month parenterally [
60]. For pregnant women after BS Kaska et al. recommend 350 μg/day sublingually or 1,000 μg/month im [
61] and Busetto et al. recommend 350 to 500 μg/day orally or 1,000 μg/month im or 3,000 μg every 6 months im or 500 μg/week intranasally [
24]. Although the available data is still conflicting, vitamin B12 deficiency seems to be associated with a higher risk of preterm birth [
68], recurrent abortion, low birth weight (LBW), intrauterine growth retardation (IUGR), neural tube defects and impaired cognitive development [
69]. Therefore, obstetricians should assess the Vitamin B12 status of pregnant women after BS every trimester and treat deficiencies accordingly [
24,
60].
Vitamin D, calcium and bone metabolism
Several studies have examined the relationship between post-BS pregnancy, calcium and vitamin D metabolism and found a Vitamin D deficiency in 3% to over 70% of pregnant women, depending on the BS procedure [
51,
54,
70]. There is a physiological increase in the need of vitamin D and calcitriol during pregnancy seemingly related to the calcium transfer to the fetus, particularly in the last trimester [
70].
Vitamin D is converted from 7-dehydrocholesterol by the skin after exposure to sunlight or provided through diet (oily fish, mushrooms, fortified cereals, egg yolks and dietary supplements). The ingested or converted vitamin D has to be activated in order to exert its functions, like increasing intestinal calcium uptake and promoting calcium and phosphate mobilization from the bone [
71,
72]. The altered anatomy of the intestinal tract occurring especially after RYGB could directly interfere with calcium absorption, possibly leading to maternal bone loss, reduced calcium levels in breast milk or deficient fetal bone mineralization [
61]. A possible association between vitamin D insufficiency during pregnancy and SGA offspring, perhaps by the impediment of intestinal calcium absorption or increase of inflammatory cytokines and cellular oxidative stress, is currently discussed [
73‐
75].
Additionally, low vitamin D levels are often associated with higher levels of parathormone, causing secondary hyperparathyroidism and increasing the risk of accelerated bone remodeling, leading potentially, among other factors, to a lower bone mineral density in bariatric patients compared to non-surgical controls [
76].
Inadequate Vitamin D levels (< 29 ng/ml) were observed in over 70% of pregnant women who underwent RYGB surgery, through all three trimesters of pregnancy and despite a supplementation with 600 IU of Vitamin D per day. The prevalence of elevated PTH levels (> 65 pg/ml) was highest in the third trimester with 32.6% of subjects. However, no adverse pregnancy outcomes were detected [
70]. A large retrospective study conducted in Taiwan pointed out that there is a high incidence of post-surgery secondary hyperparathyroidism for all procedures (37.2%) which could lead to a higher long-term fracture risk, however, the available data ins still controversial. Long term follow up of the bone’s health in patients with a history of BS should however be considered [
77]. Nutritional assessment, periodical blood examinations and aimed vitamin D supplementation are pivotal in maintaining physiological levels of vitamin D, calcium and PTH [
24,
73,
74,
78]. The current US daily consumption recommendation for vitamin D is 600 IU and the toxicity limit is estimated to be between 10,000 and 40,000 IU/day [
79]. The supplement dosage recommendations for post bariatric pregnant women range from 1,000 IU / day to 6,000 IU / day, with 1,000 to 2,000 mg of calcium citrate per day [
24,
61]. Pregnant women should be screened for Vitamin D inadequacy at least once every trimester [
23].
Other nutrients
The American Guidelines for the perioperative support of BS patients recommend routine screening for vitamin deficiencies, in order to prevent long term complications. For pregnant women, a screening every trimester is recommended [
60].
Vitamin A deficiency was reported in 10% to 58% of pregnant women after BS, depending on BS procedure and gestational age [
51,
61,
85].Vitamin A, alone or in combination with other fat-soluble vitamins (D, E, K), has to be supplied if deficiencies are present [
60,
61]. Next to being an important antioxidant in the body, Vitamin A is also involved in cell signaling pathways. There is some evidence that antenatal Vitamin A supplementation reduces the risk of maternal anemia and the risk of maternal night blindness. Furthermore there is only weak evidence that antenatal vitamin A supplementation could reduce the risk of maternal infection [
86]. The vitamin A supplement dose should not exceed 5,000 IU/day due to its teratogenic effects and should be administered in the form of beta-carotene [
24,
61,
87].
Gascoin et al. observed also vitamin E deficiency in pregnant women with a history of gastric bypass, but no adverse pregnancy outcome are described [
63].
Next to selenium, which plays an important role in several enzymatic reactions in the body, deficiencies of Vitamins C, B1 and B9 in pregnant women after BS were observed. Moreover, the offspring of mothers with a BS history displayed lower cord blood levels of several micronutrients such as Vitamin A, calcium, zinc and iron, in contrast to a control group [
63].
Because of the limited number of participants in the available studies, no practical guidelines containing thresholds or dosage recommendations for the treatment of micronutrients deficiencies in post-surgical pregnancies have been created so far [
51], however, all available statement papers recommend the supplementation of vitamins in pregnant women after BS [
23,
24,
35,
61].